1070-4272/04/7701-0005C2004 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 77, No. 1, 2004, pp. 5!10. Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 1,
2004, pp. 7!12.
Original Russian Text Copyright C 2004 by Suvorov, Fishchev, Shadricheva, Firsanova, Alekseeva.
AND INDUSTRIAL INORGANIC CHEMISTRY
Fusibility of Formulations Based on Phases of the System
Constituted by Spinel, Mullite, and Aluminum Titanate
S. A. Suvorov, V. N. Fishchev, D. B. Shadricheva, T. V. Firsanova, and N. V. Alekseeva
St. Petersburg State Technological Institute, St. Petersburg, Russia
Received January 15, 2003
Abstract-A set of physicochemical analytical methods was applied to study fusion and crystallization of
magnesia3alumina spinel, aluminum titanate, mullite, and their binary and ternary formulations. The feasibility
of elucidating phase transformations that occur when phases containing ions with variable oxidation level are
fused in an inert gas medium was analyzed.
Of particular interest in developing heat-resistant
refractory formulations are materials based on phases
of the system MgO3Al
, in which a
triangle formed by three refractory phases stands out.
These phases are magnesia3alumina spinel, aluminum
titanate, and mullite, each of which possesses unique
properties. In particular, magnesia3alumina spinel
combines high melting point (2135oC) with enhanced
resistance to the action of slag melts and high-tem-
perature strength [1, 2]. Owing to the shape of its
crystals and low thermal expansion coefficient, mul-
lite improves the heat resistance and makes higher the
softening onset temperature of refractories under
mechanical load [1, 3]. Aluminum titanate is one of a
few materials with negative thermal expansion coef-
ficient, which makes it promising as a base for struc-
tural ceramics [3, 4]. However, data on fusibility and
phase relationships in the above-mentioned three-
component system are virtually lacking.
The aim of this study was to establish the mini-
mum temperature at which a melt appears in the tri-
and to determine
how the melting occurs.
The melting points of solid phases and crystalliza-
tion temperatures of melts were determined by high-
temperature differential thermal analysis (DTA) .
The high-temperature DTA can be performed either in
a vacuum or in an inert gas. In this study, the analy-
sis was carried out in helium. To reveal the extent of
the reducing influence exerted by the inert gas medi-
um on the behavior of the basic phases in melting3
crystallization, a thermodynamic analysis of the stabil-
ity of the spinel, mullite, and aluminum titanate under
partial oxygen pressure of 0.1 Pa at 73032130oC was
made using the thermodynamic characteristics of solid
and liquid phases represented in the IVTANTERMO
database and reported in . It was found that the
magnesia3alumina spinel is stable over the entire tem-
perature range studied, mullite is unstable in the inert
medium at temperatures above 1730oC and decom-
poses into the constituent oxides, and aluminum tita-
nate is unstable below 1300oC and above 1700oC and
decomposes into TiO
. The results ob-
tained are in agreement with the data of [7, 8].
In view of the aforesaid, it was necessary, to attain
the formulated goal, to verify the adequacy of high-
temperature DTA in an inert gas as applied to oxide
compounds containing ions with variable oxidation
level. For this purpose, the process of melting of the
individual phases (spinel, mullite, and aluminum tita-
nate) and binary systems delimiting the triangle under
consideration was studied.
The tetrahedrization of the system MgO3Al
was given by Berezhnoi in . Data on
the structure of the phase diagrams of the systems
constituted by spinel and aluminum titanate, spinel
and mullite, and mullite and aluminum titanate were
reported in .
The section from spinel to aluminum titanate in the
is quasi-binary with a
eutectic containing 45 wt % MgAl
temperature of no less than 1730oC [10, 11].
The system constituted by the spinel and mullite
has a eutectic that contains 24.7 wt % spinel and melts
at 1810oC .
The section from aluminum titanate to mullite in
the ternary system Al
is not quasi-